What is GraphQL? Core Concepts

GraphQL is a query language for your API and a server-side runtime for executing those queries by using a type system you define for your data. It isn't tied to any specific database or storage engine and is instead backed by your existing code and data. Developed by Facebook and open-sourced in 2015, GraphQL offers a more efficient, powerful, and flexible alternative to traditional REST APIs.

Key Concepts of GraphQL:

• Ask for what you need, get exactly that: Unlike REST APIs that often return fixed data structures, GraphQL allows clients to specify precisely which data they require. This eliminates over-fetching (getting more data than needed) and under-fetching (needing to make multiple requests to get all necessary data).
• Single Endpoint: Typically, a GraphQL API exposes a single endpoint (e.g., /graphql). All requests, whether they are queries for data, mutations to change data, or subscriptions for real-time updates, are sent to this one endpoint. This simplifies API management and client-side logic. Understanding how APIs function is crucial in modern software; you can explore more about The Role of APIs in Modern Software for a broader context.
• Hierarchical Data: GraphQL queries naturally follow the relationships between objects in your data graph. You can request related data in a single query, mirroring the shape of the data returned.
• Strongly Typed: GraphQL APIs are defined by a schema, which describes the types of data available and their relationships. This strong typing allows for powerful developer tools, better error messages, and increased confidence in API interactions. You'll learn more about this in the GraphQL Schema and Type System section.
• Not a Storage Engine: GraphQL is a layer that sits between your client and your backend services. It uses your existing code and data sources (databases, microservices, etc.) to fulfill requests.

Imagine you're building a mobile app to display user profiles. With a traditional REST API, you might have an endpoint like /users/<id> that returns all user information, including posts, followers, and settings, even if your app only needs to display the username and profile picture. With GraphQL, your client can send a query asking for just the username and profilePicture, leading to smaller payloads and faster load times.

This client-driven approach is one of the primary reasons developers are increasingly adopting GraphQL. It empowers frontend teams to request the exact data they need, fostering more efficient and performant applications. Ready to see how this compares to REST? Check out the Advantages of GraphQL.